1. Field of the Invention
The present invention relates to an electron emission device. More specifically, the present invention relates to an electron emission device with improved image quality, a display device using the same, and/or a driving method thereof.
2. Description of the Related Art
Electron emission devices use a hot cathode or a cold cathode as an electron source. Known examples of electron emission devices using a cold cathode are field emitter array (FEA), surface conduction emitter (SCE), metal-insulator-metal (MIM), metal-insulator-semiconductor (MIS), and ballistic electron surface emitting (BSE) electron emission devices.
The FEA electron emission device is a device based on the functional principle that when a material having a low work function and/or a high beta (β) function is used as an electron source, electrons are readily emitted from the material under a vacuum by an electric field difference. A tip structure of molybdenum (Mo) or silicon (Si), or a carbon material such as graphite or DLC (Diamond Like Carbon) has been used as an electron source for the FEA electron emission device. Recently, electron emission devices using nano-materials such as nano-tubes and/or nano-wires as an electron source have also been developed.
The SCE electron emission device has a conductive film formed between first and second electrodes arranged opposing each other on a first substrate. A minute gap (or crack) is provided in the conductive film to form an electron emitter. The SCE electron emission device is based on the principle that the minute gap, i.e., the electron emitter, emits electrons when a voltage is applied to the first and second electrodes to make a current flow to the surface of the conductive film.
The MIM electron emission device and the MIS electron emission device have as their electron emitters a metal-insulator-metal (MIM) structure and a metal-insulator-semiconductor (MIS) structure, respectively. These electron emission devices emit electrons based on the principle that a voltage applied between two metals or between a metal and a semiconductor, with an insulator interposed between them, moves or accelerates electrons from the metal or the semiconductor having the higher electron potential to the metal having the lower electron potential.
The BSE electron emission device includes an electron supply layer formed from a metal or a semiconductor on an ohmic electrode, and an insulating layer and a metal film formed on the electron supply layer. This electron emission device emits electrons by the power applied to the ohmic electrode and the metal film based on the principle that electrons can be moved without being scattered when the size of the semiconductor is reduced to a range smaller than the average free stroke of the electrons.
In general, an above-described electron emission device includes an anode electrode formed on a second substrate, to which the anode electrode is applied with a high voltage having a positive voltage level, so as to cause electrons emitted from the electron emitter to collide with a phosphor formed on the second substrate.
The conventional electron emission devices are, however, problematic in that unselected pixels emit a light by a high positive voltage applied to the anode electrode. Namely, an electric field (hereinafter also referred to as “anode field”) formed around the electron emitter by the high positive voltage applied to the anode electrode causes the electron emitter to improperly emit electrons that collide with an unintended phosphor area, and hence causes a unwanted light emission on the second substrate. The unwanted light emission caused by the anode electrode can be referred to as a “diode emission.”
Also, even if the electrons are properly emitted, the conventional electron emission devices are problematic in that the electrons of the electron emitter can collide with a phosphor in an undesired area without being properly concentrated (or focused), to thereby cause a distortion of the image with a deterioration of the image quality.